This invention relates to a golf club shaft of a fiber-reinforced resin and a method of manufacturing the same, and more particularly to a golf club shaft formed so that the center of gravity of the club shaft and a kick point thereof are in the closest possible positions with respect to a grip and a club head respectively with the impact strength of the club shaft with respect to ball driving power imparted thereto, restraining an increase in the weight thereof and a method of manufacturing the same.
In general, when the weight of a golf club shaft is reduced with the length thereof left as it is, the swing balance of the club shaft can be small. As a result, the increasing of a head speed and the improving of a ball trajectory controllability are effected, and a flight distance of a ball and a flight direction stability thereof can be increased and improved respectively. When a club shaft is formed out of a lighter-weight material with the swing balance thereof unchanged, the length of the club shaft and/or the weight of a club head can be increased, so that a flight distance increasing effect can be expected.
By the way, when a wall thickness of a golf club shaft of a fiber-reinforced resin is reduced to lessen the weight thereof, the strength of, especially, a front end portion of the club shaft, which receives an impact when a ball is driven by a club head, becomes low. In order to prevent this inconvenience, a reinforcing layer of a fiber-reinforced resin is provided on the front end portion of the club shaft.
However, when a reinforcing layer of a fiber-reinforced resin is thus provided on the front end portion of a club shaft, the center of gravity of the club shaft is transferred toward a club head, and a kick point thereof toward a grip. Therefore, even when the weight of the club shaft body is reduced, a swing balance reducing effect cannot be expected much. Consequently, it is difficult to obtain the flight distance increasing and direction stability improving effects.
In order to set the impact strength of the front end portion of a club shaft not lower than a required predetermined level, it is necessary to provide thereon a plurality of reinforcing layers of a fiber-reinforced resin. This causes the specially obtained effect in reducing the weight of the club shaft body to decrease greatly.
Japanese Patent Application Kokai Publication No. 3-168168 proposes a golf club shaft of a fiber-reinforced resin provided with a tape-like film of an organic polymer as the outermost layer thereof. Providing such a tape-like film as the outermost layer of a club shaft is used as a means for securing an impact strength of the club shaft. However, since this tape-like film is provided on the whole surface of the club shaft body, the weight of the club shaft increases to a great extent accordingly, and the effect in reducing the weight of the shaft body based on the reduction of the wall thickness decreases greatly.